This invention generally relates to bearing assemblies for interconnecting a rotating body to a stationary body, and to a submersible propulsor unit incorporating such a bearing assembly. More specifically, the invention relates to a pivoted pad bearing assembly for use as a thrust bearing in a submersible propulsor unit for powering a ship, submarine or other water vessel, and a submersible propulsor unit incorporating a large diameter thrust bearing in a shroud thereof.
Pivoted or tilting pad bearings of the Kingsbury type are well known. Such a bearing assembly is typically used to transmit thrust from a rotating member, e.g., a shaft, to a stationary member such as a housing. In such an arrangement, when the shaft is rotating, thrust forces are transferred from a thrust collar to the pivoted thrust pads through a film of oil that is self-generated between the collar and the pads. Typically, the thrust force then passes from the thrust pads through support disks, leveling links and a retainer to the bearing housing and finally to a foundation or support of the apparatus. A hydrodynamic film is created and maintained due to the viscosity of the fluid, relative motion between the shaft and pads and the converging geometry of the pads. It is important that the film fully separate the thrust collar and thrust pad at all times. Otherwise, excessive drag and wear of the bearing assembly will result. Where accurate alignment of the rotating shaft with the bearing pads cannot be assured throughout all operating conditions, it is known to employ leveling links to control pivoted pad height so that the load is shared equally by all pads. Such leveling links typically comprise multiple mechanical linking members provided between each pad. Such tilting pad thrust bearings are produced, e.g., by Waukesha Bearings and described in their undated publication No. TPF-100 entitled: TILTING PAD THRUST BEARING SELECTION GUIDE.
A characteristic of pivoted pad bearing assemblies of the above-mentioned type is that the leveling action of the leveling links tends to create mechanical noise. Also, mechanical leveling links tend to be heavy and bulky and thus increase substantially the size and weight of the resulting bearing assembly. Additionally, such leveling links do not consistently provide an equal distribution of the load among the pads under all operating conditions. While these characteristics do not necessarily create problems in all applications, they create significant problems in the context of electric motor type propulsor units, as will be described in greater detail hereinafter.
One of the most advanced electric motor type propulsor units for water vehicles is disclosed and claimed in U.S. Pat. No. 4,831,297 assigned to the Westinghouse Electric Corporation (the contents of which is hereby incorporated by reference to the extent necessary for a full understanding of the present invention). This particular propulsor unit resembles a jet engine in structure and generally comprises a cylindrical shroud having a water inlet and a water outlet, a propeller having a hub rotatably mounted within the shroud on a shaft that is concentrically mounted within the shroud by a plurality of support vanes, and an electric motor for driving the propeller that includes an annular rotor mounted around the periphery of the propeller blades, and a stator that is integrated within the shroud of the unit. The advanced design of this particular prior art propulsor unit substantially increases the thrust output for a propulsor for a given weight and size while at the same time reducing the amount of noise generated due to the largely unencumbered flow of water that the propeller of the device can force through the fluid-dynamically shaped shroud. The quietness of the unit is further improved due to the noise-blocking characteristics of the shroud.
Significant refinements of the above-mentioned submersible propulsor are disclosed and claimed in co-pending commonly assigned application Ser. No. 07/571,970, filed Aug. 23, 1990 (the contents of which is hereby incorporated by reference to the extent necessary for a full understanding of the present invention). In accordance with this propulsor, as well as the propulsor in accordance with U.S. Pat. No. 4,831,297, the bearing assembly comprises both radial bearing surfaces and thrust bearing surfaces provided between a hub of the propeller means and the concentrically located shaft upon which the propeller means is rotatably mounted. Such an arrangement is perfectly adequate for a number of propulsor applications. However, this arrangement is limited with respect to the amount of bearing surface area that can be provided for the thrust bearing. Namely, since the thrust bearing surfaces must extend perpendicularly to the fluid flow direction through the propulsor, as such surfaces are increased in size, the fluid passage defined by the shroud becomes restricted.
Integral motor submersible propulsors for a number of naval applications will require the adoption of large diameter water lubricated thrust bearings. Where an integral motor propulsor is used to power a large ship such as a frigate, very high thrust requirements of the propulsor will dictate that large thrust bearing surfaces be provided in order to reduce the force per unit area of the bearing surfaces to an acceptable level. Otherwise, a thrust bearing, e.g., of the pivoted pad type, will not function properly and components may eventually fail from fatigue under excessively concentrated loads. Accordingly, there is a need for a submersible propulsor with a thrust bearing assembly which can provide greater thrust bearing surface areas without restricting fluid flow through the propulsor.
Quiet operation is a critical requirement of a submersible integral motor propulsor to be used for navy applications. As described above, known Kingsbury pivoted pad type bearings require means for leveling the height of the pads with respect to the thrust runner in order to equalize the load among the pads and thereby compensate for dimensional variations in the bearing assembly including the pad supports and thrust runner. The noise created by mechanical leveling is thus particularly detrimental with respect to navy applications of a submersible integral motor propulsor. Therefore, there is clearly a need for a means for leveling the bearing surfaces of the bearing pads which avoids the noisiness of mechanical linkages.
It is also important to minimize the size and weight of an integral motor submersible propulsor. Thus, there is clearly a need for a pad leveling mechanism which is reduced in size and weight as compared to mechanical leveling links.